The present invention relates to the field of materials handling, which involves methods and articles of manufacture for lifting, moving and otherwise handling load objects. More specifically, the present invention relates to lifting, moving and otherwise handling load objects by methods and articles of manufacture involving the use of pivot pins and other elongated members.
Cochran U.S. Pat. No. 2,271,624 suggests a type of tier-lift truck provided with a forwardly-projecting articulated bar for engaging the hollow of a bulk load and elevating same. In the manual materials-handling field, dollies having a dolly body for placing the heavy article and rolling on wheels are well known. However, where the size of the article is too unwieldy or its material is too fragile to withstand substantial handling, such dollies cannot be used at all or their size, numbers, and expense become unmanageable.
An important goal in the materials handling equipment field is profitability, which is suitably defined as the ratio of the annual profits of a business allocable to the use of the equipment to the cost of the equipment. The cost of the equipment at least includes the sum of the annual depreciation on the purchase price, plus fuel and maintenance costs, plus labor costs of using the equipment, plus allocable costs of accidents during use. Annual depreciation plus maintenance can be reduced by finding a more inexpensive design with a higher load-carrying figure of merit in a simple structure with as few moving parts as possible to do the same job. (Load-carrying figure of merit is definable as the maximum load weight capacity of the unit divided by the weight of the unit itself.) Labor costs can be reduced by finding a design which provides substantial mechanical advantage in the lifting process, high load-carrying figure of merit, reduces the number of laborers required to do a job, and reduces the time required to do the job. Costs of accidents during use can be reduced by finding a design which reduces or eliminates dangerous occupational situations and body strains which contribute significantly to the frequency, severity, and cost of accidents.
Without limiting the generality of application of the invention to be disclosed, the background of the invention is further described in the context of one specific field of application, the handling of membrane roofing rolls on the flat roofs of buildings. Such roofing membrane rolls are provided wound on hollow rigid tubes having tube ends projecting from the roll. Heretofore, the application of such rolls to roof structures has been a labor-intensive project, involving six to ten laborers lifting and positioning such rolls weighing, for instance 700 and 1400 and even 2400 pounds (more than a metric ton). The roofing membrane is a relatively soft material that can be gashed and abraded when roughly handled. Frequently, building roofs include tight spaces between constraining sidewall dimensions that complicate and slow down the roll-handling process. The roof structure of the building upon which the membrane is to be laid is frequently of limited strength, so that mechanical handling equipment cannot be very heavy if it is to be used at all; otherwise the roof structure will be punctured and significant accident damage and financial exposure will result. Time-consuming procedures of semipermanent attachment and detachment of handling equipment must be avoided and tedious positioning steps minimized. Different sizes of rolls must be movable with the same equipment.